This invention is generally directed to toner and developer compositions. More specifically, the present invention relates to toner composition with desirable fast admixing characteristics, and to processes for the preparation thereof. In one embodiment there is provided in accordance with the present invention a toner composition containing therein pigment particles having associated therewith certain charge enhancing additives inclusive of amines and quaternary ammonium salt containing compositions. Additionally, in another embodiment of the present invention there are provided processes for rapidly charging uncharged toner particles wherein there is selected for the charged developer composition toner particles, and incorporated therein pigment particles having associated therewith charge enhancing additives. The developer compositions and processes of the present invention are useful in electrostatographic and particularly xerographic imaging systems. Moreover, several of the developer compositions of the present invention are specifically useful in imaging processes having incorporated therein a Viton coated fuser roll, as these compositions are substantially compatible with such rolls in that they do not react therewith causing undesirable decomposition, and thereby adversely affecting image quality.
Developer compositions with charge enhancing additives, especially additives which impart a positive charge to the toner resin particles, are well known, reference for example U.S. Pat. Nos. 3,893,935; 3,944,493, 4,007,293; 4,079,014 and 4,394,430. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of certain quaternary ammonium salts as charge control agents for electrostatic toner compositions. In accordance with the disclosure of this patent, certain quaternary ammonium salts, when incorporated into a toner material, provide a composition which exhibited relatively high uniform stable net toner charge when mixed with a suitable carrier vehicle.
Further, there is disclosed in U.S. Pat. No. 4,338,390 developer and toner compositions having incorporated therein as charge enhancing additives organic sulfate and sulfonate substances. A similar disclosure is present in U.S. Pat. No. 4,394,430.
Moreover, there is disclosed in U.S. Pat. No. 4,298,672 positively charged other compositions with resin particles, and pigment particles, and as a charge enhancing additive, alkyl pyridinium compounds, inclusive of cetyl pyridinium chloride. While the developer compositions disclosed in the '672 patent are sufficient for their intended purposes, it appears that the alkyl pyridinium compounds involved may react with the polymer present on Viton fuser rolls causing decomposition thereof. Also, several other charge control agents disclosed in the prior art interact with Viton fuser rolls used in electrostatographic imaging systems. This interaction causes the fuser roll to be adversely affected resulting in the deterioration of image quality. For example, Viton fuser rolls discolor and turn black, and develop multiple surface cracks and harden when certain charge control additive compounds are present in the toner mixtures. Apparently, these charge enhancing additives are not permanently retained by the toner resin particles, that is, they are leachable therefrom and deposit on the Viton fuser roll causing decomposition thereof. This leaching problem is substantially eliminated with the toner and process of the present invention.
One Viton fuser roll selected for use in electrostatographic copying machines is comprised of a soft roll fabricated from lead oxide and DuPont Viton E-430 resin, a vinylidene fluoride hexafluoropropylene copolymer. This roll contains approximately 15 parts of lead oxide and 100 parts of Viton E-430 which mixture is blended and cured on the roll substrate at elevated temperatures. Apparently, the function of the lead oxide is to control the generation of unsaturation by dehydrofluorination which can cause crosslinking, and to provide release mechanisms for the toner composition. Excellent image quality has been obtained with Viton fuser rolls, however, in some instances there results a toner fuser compatibility problem when charge control agents are part of the toner mixture. For example, as indicated herein, it appears that certain specific charge enhancing additives react with Viton when these additives are not permanently retained on the toner resin particles. In view of this, the Viton fuser roll may turn black, develop multiple surface cracks, and the surface thereof may harden, thereby resulting in image quality deterioration.
Additionally, in order to immediately obtain images of high quality in most xerographic imaging systems upon addition of new uncharged toner particles to the charged developer, it is necessary for these particles to acquire the appropriate charge polarity and charge magnitude. Acquiring this charge can consume a period of in excess of five minutes to about 15 minutes; thus in many instances, initial copies obtained from xerographic imaging apparatuses are of an inferior quality as compared to images obtained thereafter. Once the uncharged developer composition has acquired the appropriate charge, image quality improves. Thus some effort has been directed to providing compositions and processes wherein the uncharged toner particles added to an imaging apparatus will acquire charge of the appropriate magnitude and polarity in a period substantially less than ten minutes. In some instances, no satisfactory images whatsoever can be developed until the uncharged toner is mixed with the charged toner present in the imaging apparatus for a period of from about 10 to 15 minutes mixing time. The period of time within which the uncharged toner acquires the required charge is referred to as admix charging.
There is described in several patents, including U.S. Pat. No. 4,304,830, toner compositions and processes for enabling uncharged toner particles to be charged in a period of from about one minute to about five minutes. According to the teachings of this patent, there is selected for imparting charges to the uncharged toner particles a developer composition containing therein as an important component an alkyl pyridinium charge enhancing additive. Accordingly, when the alkyl pyridinium compound is present, the rate at which the uncharged toner acquires charge, such as a positive charge, is substantially less than ten minutes. Typically, the uncharged toner particles become suitably charged within a period of time of from about one minute to about five minutes, and usually less than about 10 minutes. Such rapid admix charging allows developer systems to be more stable over a shorter priod of time, therefore, better quality images are obtained with no background according to the teachings of this patent.
Therefore, there is a need for improved processes, and improved toner compositions, wherein rapid admix charging can be achieved. There also continues to be a need for toner compositions and processes wherein the charge enhancing additive selected is substantially permanently retained on the toner pigment particles. Also, there is a need for processes that enable uncharged toner particles to acquire a proper charge level and an appropriate polarity in a period of less than about five minutes. Moreover, there remains a need for improved toner compositions that are compatible with fusing rolls incorporated into imaging apparatuses, especially Viton fuser rolls. Further, there remains a need for attaining positively charged toners by simplified methods wherein the pigment particles selected are associated with certain charge enhancing additives. There also remains a need for toner compositions with selected desirable dispersion of pigment particles therein.